Tachometer Disadvantages

Thread Starter


Joined Aug 12, 2010
Hi All,

I'm doing some coursework on an Inverter Fed Induction Motor, and have been posed the question:

'What are the practical disadvantages of using a tachometer?'

The tachometer had a digital read out, but other than that I don't know anything about it. Do I need to know more to say where the disadvantages would lie, or are there generic issues with tachometers?

Thanks for your help!



Joined Oct 3, 2010
When you say "tachometer" I think Analog Output Brushed Tachogenerator (like in industrial drive applications), so my answers are based on that:

Tachometers have brushes, which wear, and need to be maintained.
Tachometers have magnets, which can weaken over time, or if overheated, and cause erroneous measurements.
Tachometers output an analog voltage, which is proportional only to speed, so rotor angle cannot be determined like with an encoder.
Due to the analog voltage, they are also suceptible to loading effect, depending on the input impedance of the measurement device or other factors in the circuit, especially at low speed.
Not as accurate as an encoder, especially at low speed.
analog tachometers generally cost more than encoders because they are more material-intensive, and also due to being phased out in favor of encoders; hard to find and expensive when you find them